tapestry/tapestry-framework/src/java/org/apache/tapestry/services/impl/EngineFactoryImpl.java

// Copyright 2004, 2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package org.apache.tapestry.services.impl;

import org.apache.hivemind.ApplicationRuntimeException;
import org.apache.hivemind.ClassResolver;
import org.apache.hivemind.ErrorLog;
import org.apache.tapestry.IEngine;
import org.apache.tapestry.engine.BaseEngine;
import org.apache.tapestry.services.EngineFactory;
import org.apache.tapestry.spec.IApplicationSpecification;

import java.util.Locale;

/**
 * Standard implementation of {@link org.apache.tapestry.services.EngineFactory} service. This
 * should do for most purposes, since a major focus of Tapestry 4.0 is to no longer require
 * subclassing of {@link org.apache.tapestry.engine.BaseEngine}.
 * 
 * @author Howard Lewis Ship
 * @since 4.0
 */
public class EngineFactoryImpl implements EngineFactory
{
    private IApplicationSpecification _applicationSpecification;

    private String _defaultEngineClassName;

    private EngineConstructor _constructor;

    private ClassResolver _classResolver;

    private ErrorLog _errorLog;

    /**
     * Creates a new engine?
     * @author Howard Lewis Ship
     */
    interface EngineConstructor
    {
        IEngine construct();
    }

    // TODO: Create a BaseEngineConstructor that is hardcoded to
    // instantiate a BaseEngine instance, without using reflection
    // (for efficiency).

    /**
     * Creates a new reflective engine constructor.
     */
    static class ReflectiveEngineConstructor implements EngineConstructor
    {
        private Class _engineClass;

        ReflectiveEngineConstructor(Class engineClass)
        {
            _engineClass = engineClass;
        }

        public IEngine construct()
        {
            try
            {
                return (IEngine) _engineClass.newInstance();
            }
            catch (Exception ex)
            {
                throw new ApplicationRuntimeException(ImplMessages.errorInstantiatingEngine(_engineClass, ex), ex);
            }
        }
    }

    public void initializeService()
    {
        String engineClassName = _applicationSpecification.getEngineClassName();

        // TODO: Check in web.xml first.

        if (engineClassName == null)
            engineClassName = _defaultEngineClassName;

        Class engineClass = _classResolver.checkForClass(engineClassName);

        if (engineClass == null)
        {
            _errorLog.error(ImplMessages.engineClassNotFound(engineClassName), null, null);
            engineClass = BaseEngine.class;
        }

        _constructor = new ReflectiveEngineConstructor(engineClass);
    }

    public IEngine constructNewEngineInstance(Locale locale)
    {
        IEngine result = _constructor.construct();

        result.setLocale(locale);

        return result;
    }

    public void setApplicationSpecification(IApplicationSpecification specification)
    {
        _applicationSpecification = specification;
    }

    public void setClassResolver(ClassResolver resolver)
    {
        _classResolver = resolver;
    }

    public void setDefaultEngineClassName(String string)
    {
        _defaultEngineClassName = string;
    }

    public void setErrorLog(ErrorLog errorLog)
    {
        _errorLog = errorLog;
    }

}